This invention relates to electromagnetic projectile launching systems and more particularly to such systems which use a cylindrical rail arrangement to accelerate the projectile.
Electromagnetic projectile launchers are known which comprise a pair of conductive rails, a sliding conductive armature between the rails, a source of high current, and means for commutating this current into the rails and through the armature. This places an electromagnetic force on the armature which propels it along the conductive rails. An early launcher employing this concept is disclosed in U.S. Pat. No. 1,370,200, dated Mar. 1, 1921.
Present electromagnetic projectile launchers utilize a pair of parallel rectangular rails to accelerate a projectile. Copending application Ser. No. 185,706, filed Sept. 10, 1980, now U.S. Pat. No. 4,369,691, entitled "Projectile Launching System With Resistive Insert in the Breech", and assigned to the present assignee, illustrates a launcher with parallel rectangular rails. The distribution of current in the rails and armatures of these launchers is non-uniform because of the skin effect. Current concentrates on the rail surfaces and rail corners leading to intense local heating in the rails and armature. Since there is no way to rotate the projectile during launching, fins must be used as stabilizers. In addition, the leakage of magnetic flux from the vicinity of the launcher assembly provides a magnetic signature which may be detectable at significant distances from the launcher. The reduction of this magnetic signature is essential in some applications.
The present invention seeks to achieve a more uniform current distribution in the launcher rails, reduce magnetic signature, and provide means for spin stabilization of the projectile. These objectives are achieved by two different cylindrical launcher configurations.
The first configuration comprises a barrel with multiple rails located along the inner surface. These rails are connected to a source of high current such that current flows in the opposite direction in any two adjacent rails. A plurality of conductive armatures are located between the rails and attached to the periphery of a core such that a high current in the rails and armatures electromagnetically propels the core and armatures along the barrel. This configuration reduces the far magnetic field signature to a multi-pole field which will be considerably less that of a single two parallel rail geometry.
By twisting the conductors, the barrel can be effectively rifled. This will impart a spin to the core during launch which can be transferred to a projectile by a splined or keyed shaft, thereby providing spin stabilization for the projectile.
The second configuration comprises a cylindrical outer rail with a coaxial cylindrical inner rail. Conductive armatures are located between these rails and are propelled along them when a high current flows in the rails and armatures. A projectile is driven by a plug located within the inner rail. This plug is connected to the armatures by rigid insulating supports which pass through axial slots in the inner rail. By twisting the slots, spin can be imparted to the plug during launch. This spin can be transferred to a projectile by a splined or keyed shaft, thereby providing spin stabilization for the projectile.
Alternatively, a liquid can be used to couple armature movement to a projectile. The liquid would be located within the cylindrical rails such that movement of the armature would force liquid from the space between the cylindrical rails into the center of the inner cylindrical rail, thereby moving the projectile. This second configuration virtually eliminates far magnetic field signature.
Each of these configurations can be constructed with augmenting rails to increase projectile force for a given current. A launcher employing the augmenting rail concept is disclosed in copending application Ser. No. 137,059, filed Apr. 3, 1980, now U.S. Pat. No. 4,347,463, entitled "Electromagnetic Projectile Launcher With Self-Augmented Rails", and assigned to the present assignee.